In recent years, there is a strong demand in improving durability of polymer materials which are used under severe circumstances such as outdoors from the viewpoints of reducing maintenance cost and reducing environmental load by saving resources.
Among them, in the field of a paint, it is intended to change from a solvent-based paint which uses an organic solvent as a medium to a water-based paint which uses water as a dispersing medium, and the use of the water-based paint is rapidly expanding. Consequently, demands for the performance of the water-based paint have become high degree, and water-based paints having high-degree weather resistance have been proposed.
For example, there is a description, in Patent Document 1, that a paint, which is made by copolymerizing an ultraviolet light absorber (hereinafter, expressed as a “reactive UVA”) having an unsaturated double bond, in a molecule, capable of radical polymerization, with a polymerizable monomer having a highly hydrophobic cyclohexyl group, having excellent weather resistance for a long time without showing the bleed out of the UVA component from the coating film can be obtained.
In Patent Document 2, there is a description that a paint, which is made by copolymerizing a hindered amine type light stabilizer (hereinafter, expressed as a “reactive HALS”) having an unsaturated double bond in a molecule and a polymerizable monomer having a highly hydrophobic cyclohexyl group, having excellent weather resistance for a long time without showing the bleed out of the HALS component from the coating film can be obtained.
Further, in Patent Document 3, there is a description that a paint composed of an emulsion obtained by copolymerizing a reactive HALS at the last stage of a multistage emulsion polymerization in the presence of a silane coupling agent having a cyclohexyl group is excellent in compatibility and film formability, and excellent weather resistance for a long time can be obtained.
Further, in the field of a water-based paint, investigations concerning a weather resistance improver have been carried out to improve only weather resistance of a water-based paint with relatively low weather resistance, which has been conventionally used, without changing physical properties of the water-based paint. However, as to the water-based paint, there has been a problem, in stability of quality of the water-based paint, in which, for example, the weather resistance improver comes to bleed with time on the upper layer when the weather resistance improver is added because the main medium of the water-based paint is water. Further, there has been a problem that the water-based paint does not realize sufficient performance even in the case of forming a film using the water-based paint right after it is stirred because it is difficult to homogeneously disperse the weather resistance improver.
As countermeasures to these problems, in Patent Document 4, a technology has been proposed, in which a nonreactive UVA or a nonreactive HALS which does not have an unsaturated double bond in a molecule is previously dispersed in water using an emulsifier and then the resultant dispersion is added to the water-based paint to improve weather resistance of the water-based paint.
Further, in the field of a thermoplastic resin to be used for automobiles and building materials, a weather resistance improver such as HALS, UVA, or an antioxidant in accordance with characteristics of each thermoplastic resin has been proposed. However, in the case of the weather resistance improver having relatively low molecular mass, it is difficult to maintain capability for improving weather resistance for a long time owing to bleed out of the weather resistance improver with time, which results in concentration lowering of the weather resistance improver in a base material. To solve such a problem, a polymer type weather resistance improver has been proposed. In Patent Document 5, a technology of improving weather resistance of a thermoplastic resin has been proposed, in which a reactive UVA and a reactive HALS are copolymerized in high concentration in an organic solvent and the resultant mixture is reprecipitated in a poor solvent to recover the polymer type weather resistance improver which is then compounded into the thermoplastic resin.
Patent Document 1: Japanese Patent Application Laid-Open No. Hei 8-198,130
Patent Document 2: Japanese Patent No. 2,637,574
Patent Document 3: Japanese Patent Application Laid-Open No. 2004-10,805
Patent Document 4: Japanese Patent Publication No. Hei 3-46,506
Patent Document 5: Japanese Patent Application Laid-Open No. 2003-40,937